Variation in Coastal and Insular Slash Pine of Mississippi and Alabama

Abstract

Variations from north to south were found among 27 needle, twig, bud, and cone characters from 11 island, coastal, and inland collections of Pinus elliottii Engelm. The variations were typical of those expected for both environmental and genetic responses to progressively more severe habitats. The trends were partially confirmed by progeny tests and their intensity varied with longitude. When compared to the south Florida variety, the Gulf Coast variety was distinct from it. Deviations from commonly accepted characteristics were noted for both varieties. INTRODUCTION For studying the nature and results of gene action, geneticists often prefer isolated populations to the main body of a species. The offshore islands in the Gulf of Mexico afford such populations of slash pine (Pinus elliottii Engelm.) for biosystematic comparisons with coastal and inland sources. The islands and the immediately adjacent coast are both sandy, and the trees appear similar. The coastal trees are favorites of seed collectors because of their general shortness, gum-drop shaped crowns, and prolific cone crops. It is important in tree improvement to learn if they are genetically different from those further inland, and to determine if coastal and island trees are morphologically similar to trees of the south Florida variety (Pinus elliottii var. densa Little and Dorman), which they superficially resemble. Wakeley (1961) considered that the major variation among slash pine sources was caused by infiltration of genes of the south Florida variety to that of central Florida. The present study is a step in solving these problems. The part of the island chain under investigation, which includes Cat, Horn, and Dauphin islands, extends for approximately 70 miles parallel to the coast (Fig. 1). Distance to the coast varies from 7 to 10 miles. McGee (1891) considered that the islands were formerly part of the mainland and that the present water areas were formed by the sinking of the land. In contrast, Moore (1961) believed the islands were built up some five or six thousand years ago after the sea level became stabilized at or near its present height. A similar conclusion was reached by Devries1 (personal communication), using information on sea levels published by Fairbridge (1961). However, 1 Geologist, Gulf Coast Research Laboratory.